From b4ef20d71666f5d2d9a6fa2af137a1012aed9a4f Mon Sep 17 00:00:00 2001
From: alan1001110 <alan1001110@gmail.com>
Date: Sat, 17 Aug 2019 05:40:54 -0700
Subject: [PATCH] replaced stub with solution to large sum (#36618)

replaced stub with solution to large sum, explanation, links
---
 .../problem-13-large-sum/index.md             | 32 +++++++++++++++++--
 1 file changed, 29 insertions(+), 3 deletions(-)

diff --git a/guide/english/certifications/coding-interview-prep/project-euler/problem-13-large-sum/index.md b/guide/english/certifications/coding-interview-prep/project-euler/problem-13-large-sum/index.md
index 1dd8d595fa7..0b3444a2d63 100644
--- a/guide/english/certifications/coding-interview-prep/project-euler/problem-13-large-sum/index.md
+++ b/guide/english/certifications/coding-interview-prep/project-euler/problem-13-large-sum/index.md
@@ -1,10 +1,36 @@
 ---
 title: Large sum
 ---
+
 ## Problem 13: Large sum
+Challenge: Work out the first ten digits of the sum of one-hundred 50-digit numbers.
 
-This is a stub. <a href='https://github.com/freecodecamp/guides/tree/master/src/pages/certifications/coding-interview-prep/project-euler/problem-13-large-sum/index.md' target='_blank' rel='nofollow'>Help our community expand it</a>.
+## Spoiler Alert!
 
-<a href='https://github.com/freecodecamp/guides/blob/master/README.md' target='_blank' rel='nofollow'>This quick style guide will help ensure your pull request gets accepted</a>.
+## One Solution:
+```
+function largeSum(arr) {
+  let sum = arr.reduce((acc, item) => acc + Number(item), 0);   // 8.348422521139211e+49
+  let str = sum.toString().split('e')[0];   // '8.348422521139211'
+  return 1e+9 * str.slice(0,11);   // 8348422521
+}
 
-<!-- The article goes here, in GitHub-flavored Markdown. Feel free to add YouTube videos, images, and CodePen/JSBin embeds  -->
+const testNums = [
+  '37107287533902102798797998220837590246510135740250',
+  '46376937677490009712648124896970078050417018260538'
+];
+
+largeSum(testNums);
+```
+### Code Explanation:
+
+*   The function receives an array of strings
+*   The first line converts the strings to numbers and adds them 
+*   The second line converts the large sum to a string with toString, then gets everything to the left of 'e' using String.split().
+*   The third line multiplies 1,000,000,000 by the first 11 characters to implicitly coerce the string to a 10 digit number
+*   Note: One regular expression could accomplish the same task as the second and third lines together
+
+### Resources
+
+*   <a href='https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/reduce' target='_blank' rel='nofollow'>Array.reduce()</a>
+*   <a href='https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/split' target='_blank' rel='nofollow'>String.split()</a>